The aim of this study was to compare responses to cold stress in newborn lambs and kids. Two experiments were conducted in a climatic chamber with controlled air temperatures and artificial wind and rain. The first experiment involved 25 Poll Dorset × (Border Leicester × Romney) lambs and 16 Angora × feral kids while the second involved 30 Suffolk × (Border Leicester × Romney) lambs and 26 Angora × feral kids. Rectal temperatures were measured and the rate of decline in rectal temperature estimated in both experiments. In the second experiment, metabolic rate was also measured and coat characteristics (birth coat depth and wool weight per unit area of skin) were examined. The effects of birth rank and sex on resistance to cold exposure and their interaction with species were examined in both experiments.

In experiment 1, kids had lower rectal temperatures than lambs at the start of the test but there was no species effect on the rate of decline in rectal temperature. In experiment 2, kids exhibited a significantly greater rate of decline in rectal temperature than did lambs. This difference in species effect between the experiments reflected primarily a greater rate of body cooling in the Poll Dorset-cross lambs (experiment 1) than in the Suffolk-cross lambs (experiment 2) rather than a difference between the kids in the two experiments. Additionally, in experiment 2, metabolic rate per unit live weight was significantly lower in the kids than in the lambs. No differences were apparent between the species in coat characters. Multiple-born lambs and kids were found to exhibit a significantly greater rate of decline in rectal temperature than singles, but only marginal differences in heat production were observed between the birth ranks. No significant effects of sex on resistance to cold stress were found in this study. Effects of birth rank and sex were additive with those of species. It is concluded that a combination of low heat production capacity and small body size is responsible for the generally poor responses of newborn kids to cold stress but there is probably little difference between lambs and kids in the insulative value of their birth coats.